Tri-leaflet one-way valves are well-known in the art and are commonly used in heartlung machines, heart-assist devices and as surgical prosthetic implants to replace the heart's natural valves. Such valves must have sufficient strength and resiliency to maintain their shapes and operate securely through a great many cycles, without substantial wear or failure. At the same time, the leaflets must be sufficiently flexible to open and close smoothly, with minimal pressure drop across the valve and without creating undue turbulence or hemolytically damaging the blood cells. Various materials have been used for this purpose, including primarily hemocompatible polyurethane of different grades, as well as silicones, Teflon.TM. and other polymers. Complex, time-consuming processes must generally be employed in order to produce valves having the desired properties. Exemplary prior art patents describing valves of this sort and methods of producing them include U.S. Pat. No. 4,192,020, to Davis, et al.; U.S. Pat. No. 4,222,126, to Boretos, et al.; U.S. Pat. No. 4,629,459, to Ionescu, et al.; and U.S. Pat. No. 4,888,009, to Lederman, et al., which are incorporated herein by reference.
U.K. patent application GB 2,255,394A, by Rottenberg, et al., which is assigned to the assignees of the present invention and is incorporated herein by reference, describes an integral tri-leaflet valve- sleeve structure and a method of producing the structure by injection molding. The structure includes a cylindrical outer sleeve, from which three flexible, fabric-reinforced leaflets extend radially inward, meeting in the center when in the closed position. Fluid pressure exerted on the valve from one end of the cylinder causes the valve to open and allows blood to flow through the cylinder in a desired direction. When the pressure is released, or when pressure is exerted from the opposite end of the cylinder, the valve closes and prevents back-flow of blood in a reverse direction.